Formed in 1908, the FBI has the broadest investigative authority of all federal law enforcement agencies. The agency leads long-term, complex investigations, while working closely with other federal, state, local, and foreign law enforcement and intelligence agencies.

An FBI special agent is faced with the challenge of investigating and upholding certain federal laws that come under the FBI's jurisdictions. Throughout their careers, FBI agents conduct investigations on a variety of issues in the following categories: counterterrorism, counterintelligence, cyber investigations, public corruption, civil rights, organized crime, white-collar crime (such as antitrust investigations, bankruptcy fraud, environmental crime, financial institution fraud, government fraud, health care fraud, insurance fraud, money laundering, securities/commodities fraud, and telemarketing fraud), and major thefts/violent crimes (such as art theft, crimes against children, jewelry and gem theft, and Indian Country crime). FBI agents may be assigned to a wide range of investigations, unless they have specialized skills in a certain area. In short, agents are assigned to a case, conduct an investigation, and then submit a report of their findings to the U.S. Attorney's Office.

During an investigation, agents may use a vast network of communication systems and the bureau's crime detection laboratory to help them with their work. Agents may gather information with the help of the National Crime Information Center and the Cyber Division. Once they have information, agents must make sure the facts and evidence are correct. FBI agents may discuss their findings with a U.S. attorney or an assistant U.S. attorney, who decides whether the evidence requires legal action. The Justice Department may choose to investigate the matter further, and the FBI agents may obtain a search warrant or court order to locate and seize property that may be evidence. If the Justice Department decides to prosecute the case, the agent may then obtain an arrest warrant.

With the goal of gathering information and reporting it, FBI agents may spend a considerable amount of time traveling or living in various cities. Their investigations often require the agent to interview people—witnesses, subjects, or suspects—and search for different types of records. Agents may set up a stakeout to watch a place or person. Special agents may also work with paid informants. Sometimes agents testify in court about their investigations or findings. If enough incriminating evidence is found, FBI agents conduct arrests or raids of various types. Agents must carry firearms while on duty, and they typically carry their bureau identification badge. Agents always carry their credentials. Most of the time they wear everyday business attire—not uniforms.

Some agents with specialized skills may work specific types of investigations, such as fraud or embezzlement. Language specialists—who can be employed as special agents or support personnel—may translate foreign language over a wiretap and recordings into English. The FBI also employs agents specializing in areas such as chemistry, physics, metallurgy, or computers. Laboratory specialists analyze physical evidence like blood, hair, and body fluids, while others analyze handwriting, documents, and firearms. Behavioral science specialists profile serial murderers, rapists, and other criminals committing patterned violent crimes.

Agents often work alone, unless the investigation is particularly dangerous or requires more agents. However, FBI agents do not investigate local matters—only federal violations that fall within their jurisdiction. The agents' work can be discussed only with other bureau employees, which means they cannot discuss investigations with their families or friends.

The FBI operates 56 field offices, approximately 380 resident agencies, and nearly 80 foreign legal attaché offices. FBI agents must be willing to be reassigned at any point in their career.